Apparatus for and method of manufacturing semiconductor wafer

ABSTRACT

When an ingot is sliced into wafers, they are given serial numbers for identification. This makes possible to identify which any wafer being processed is of those sliced from the ingot no matter where the wafer is in a manufacturing process. Each wafer is traced so as to determine the path along which the wafer was transferred during the manufacturing process, and results are stored as wafer information.

TECHNICAL FIELD

The present invention relates to an apparatus for and method ofmanufacturing semiconductor wafers and more particularly, to tracing ofmanufacturing history.

BACKGROUND ART

For semiconductor wafers of silicon, germanium, gallium arsenide (GaAs),etc. for use as the material of IC, LSI or the like, a higher quality ofthe wafers has been demanded year after year as highly integrateddevices are required.

Even when semiconductor wafers are processed by the same processingmachine, the quality of each of the wafers may differ to such an extentthat badly affects a non-defective rate. Accordingly, for the purpose ofimproving the quality, it is necessary to accumulate such data that showa correlation between quality and working conditions on the wafer basis.

Conventionally, semiconductor wafers are manufactured on a lot basis (agroup of about 20-300 wafers having same characteristics required), andquality information including operation results are managed usually inthe form of a daily report in which the quality information is listed byan operator on a lot basis.

However, this method has a problem that important wafer-based qualityinformation such as, from which position of a material ingot, a waferwas cut out, by which thermal treatment machine, the wafer wasprocessed, at which position of a bath of a cleaning equipment, thewafer was cleaned, etc. cannot be managed, thus resulting in lack of thenecessary information for quality improvement. Further, since themanagement of the quality information is manually carried out in thismethod, this results in reduction of the reliability of the informationand in the increased number of necessary management steps.

Furthermore, since the management is carried out on a lot basis, in thecase where the next step is such a batch processing step as a cleaningor chemical treatment step, the processing cannot proceed to the nextstep until one-lot processing is finished, which results in the factthat a wait time is increased and thus a processing time includes auseless waste time, which impedes, in particular, cost reduction in arecent tendency of small number/multiple sorts of items production.

In general, for the purpose of managing objects to be processed on anindividual basis, there is employed such a method that a bar code ormarker is applied to each of the objects and object management iseffected on the basis of the bar code or mark as an identificationsymbol. When the objects are semiconductor wafers, however, suchapplication of the identification mark to the wafer in the above methodis not preferable from the viewpoint of quality.

For example, such bar code becomes one of serious pollution sources atthe time of cleaning the wafers. Further, when laser marking is carriedout, the mark must be made fairly deep, which might involve fluctuationsin the wafer characteristics caused by a high level of laser energy. Inaddition, pollution substances tend to accumulated in the marks, whichmight lead to undesirable influences on other wafers. And some productsmust be subjected to such a step that the marking is never allowed.

In this way, the conventional method has a problem that wafer-basisquality information cannot be managed easily and sufficiently.

DISCLOSURE OF THE INVENTION

In view of such circumstances, the present invention has been made toprovide an apparatus and method for manufacturing semiconductor waferswhich, with respect to each of the wafers to be processed, can identify,at any stage of processing steps, to what numbered wafer the cut-outwafer corresponds in a material ingot, and under what conditions thewafer was so far subjected to treatments.

That is, an object of the present invention is to provide an apparatusand method for manufacturing semiconductor wafers, which can manageeasily and sufficiently quality information of any sorts of wafers on anindividual basis.

In accordance with an aspect of the present invention, there is provideda method for manufacturing semiconductor wafers, in which anidentification number is set for each of the semiconductor wafers, theidentification numbers are stored in a storage medium as identifierinformation, a processing path as new identifier information indicativeof how the wafer was transferred and how the wafer was processed in eachof wafer manufacturing steps is traced on each wafer basis inassociation with the identifier information in a previous step and thenew identifier information are additionally stored in the storage mediumas wafer information, and management is carried out over history of eachwafer throughout the entire wafer manufacturing steps on the basis ofthe stored wafer information.

In accordance with another aspect of the present invention, there isprovided an apparatus for manufacturing semiconductor wafers whichcomprises identification number applying means for setting anidentification number for each of the semiconductor wafers and forstoring the identification numbers in a storage medium as identifierinformation, wafer information storing means for tracing as newidentifier information a processing path indicative of how the wafer wastransferred and how the wafer was processed in each of wafermanufacturing steps on each wafer basis in association with theidentifier information in a previous step and for additionally storingthe new identifier information as wafer information in the storagemedium, and wafer history management means for performing managementover history of each wafer throughout the entire wafer manufacturingsteps on the basis of the stored wafer information.

In the invention, for example, an identification number is applied toeach of wafers cut out from a material ingot in their cut-out order, theprocessing path indicative of how each wafer was transferred in each ofthe manufacturing steps is traced and then stored as the waferinformation.

It is desirable that the processing path be expressed in terms of anumber of a manufacturing machine and wafer positional coordinates in ajig.

Further, as the storage medium, a computer and a computer network areutilized.

In accordance with the present invention, since wafer identification canbe realized on each wafer basis, wafer quality management can bereliably realized on each wafer basis with a less number of steps.

Further, since the need for management based on each lot can beeliminated and management based on each wafer can be realized, even whenthe next step corresponds to such a batch processing step as a cleaningstep or a chemically processing step, the wafer can be shifted to thenext step on each processing-batch basis, a processing waste time can bereduced, and the invention can be effectively applied to smallnumber/multiple sorts of items production.

Also since the wafer identification can be carried out while eliminatingthe need for applying to the wafer such external identifier informationas a marker by means of printing or laser, the deterioration of thewafer quality caused by such marking can be avoided.

When processing result data are accumulated on each wafer basis, waferdefect factors can be closely found, which leads to an increased wafernon-defective rate.

In addition, since such a wafer physical characteristic as an electricresistance can be presented on each wafer basis, even when it is desiredto build a device in the wafer, close adjustment can be achieved andthus this leads to an improved non-defective rate of the device itself.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 schematically shows a management system in accordance with anembodiment of the present invention;

FIG. 2 shows a single crystalline silicon for use in the presentinvention;

FIG. 3 shows a transporter for use in the embodiment of the presentinvention;

FIG. 4 shows identification data for use in the embodiment of thepresent invention;

FIG. 5 shows a circular plate for use in the embodiment of the presentinvention;

FIG. 6 is a block diagram of a lapping machine for use in the embodimentof the present invention;

FIG. 7 shows an example of how wafers are mounted on the circular plateused in the embodiment of the present invention;

FIG. 8 shows identification data for use in the embodiment of thepresent invention;

FIG. 9 shows a cleaning machine for use in the embodiment of the presentinvention; and

FIG. 10 shows an inspection system for use in the embodiment of thepresent invention.

BEST MODE FOR CARRYING OUT THE INVENTION

An embodiment of the present invention will be detailed with referenceto the accompanying drawings.

Referring to FIG. 1, there is shown a schematic arrangement showingsteps of a silicon wafer manufacturing method in accordance with anembodiment of the present invention.

The silicon-wafer manufacturing method includes a lifting step 1 forforming a material ingot with use of a Czochralski (CZ) method ofgrowing a cylindrical crystal from a material (silicon) melt within acrucible, a slicing step 2 for cutting the material ingot into wafers, aheat treatment step 3 for removing crystal defects or the like, alapping step 4 for polishing surfaces of the wafers into accurate mirrorsurfaces, a cleaning step 5 for cleaning the mirror-polished wafers toremove from the wafers such deposits adhered on the surfaces of thewafers as dust and chemicals, and an inspection step 6 for inspectingthe conditions of these processing steps to check non-defective anddefective wafers or to perform feed-back of quality information. Thesesteps 1 to 6 are connected with a computers 11 for management of thelifting step, a computer 21 for management of the slicing step, acomputer 31 for management of the heat treatment step, a computer 41 formanagement of mirror-polishing step, and a computer 61 for management ofthe inspection step respectively to manage the transportation path andquality information of each wafer with respect to each of the steps andto inform the other steps of the management result. The computers formanagement of the respective steps are also connected to a host computer7 through a computer network 8 known as LAN, at which a correspondencebetween the quality information reported on the wafer basis andassociated wafers is made and a put into a database.

More in detail, first of all, when such a silicon ingot as shown in FIG.2 is formed in the lifting step, the ingot is cut into wafers in theslicing step 2, at which time numbers are sequentially set at the wafersin the cut-out sequence. The cut-out wafers are individually separatelyhoused in such a transport jig (carrier) as shown in FIG. 3. In thiscase, the numbers of grooves of the transport jig, the numbers of thehoused wafers, and the number of the jig are recorded in a relationshipmutually related to one another, and the recorded information isinformed to the other steps through the computer network 8. As a result,as shown by exemplary identification data in FIG. 4, identificationbetween the wafers can be expressed in terms of the positions of thegrooves. In the case where the wafers are automatically housed into theassociated grooves of the transport jig, correlation between the groovesand wafers is automatically made. In the case where the wafers aremanually housed into the grooves of the transport jig, the waferidentification can be realized by reading it by means of bar code readeror an image recognizer.

The wafers cut in the slicing step 2 in this manner are housed in thetransport jig and again housed in a heat treatment jig. In this case, ifthe wafers after subjected to the heat treatment step are again housedinto the transport jig from the heat treatment jig with the initialhousing positions of the wafers kept, then the wafers remain in anidentifiable state.

In the lapping step, further, the wafers fed from the heat treatmentstep and being housed in the transport jig are one by one bonded onwafer-lapping jigs. In this step, e.g., about 4-10 wafers are separatelybonded on such a circular plate having a marker M as shown in FIG. 5.About 4 of such plates having wafers bonded thereon are rotated togetherto cause the wafers to be slid at their one side surfaces with respectto an abrasive cloth, while an abrasive agent is applied to the wafersto polish the wafers. Accordingly, when the wafers are bonded on thecircular plate sequentially from the position of the marker M, thewafers can be easily identified even after the rotation of the plate.

The above processing operations will be explained in the following. Asshown in FIG. 6, the position of the marker M is detected by a platepositioning mechanism 401 and then modified so that the marker M isinitially located at the wafer bonded position.

Under such a condition that the position of the plate is rotatablymodified so that the first-wafer bonding position comes at a bondingmachine 402 side, the wafers are sequentially bonded with use of thebonding machine 402. In this case, as shown in FIG. 7, identificationnumbers are set for the wafers sequentially in the plate rotationaldirection in relation as their wafer numbers. And the number of theplate is read out with use of a bar code reader or an image recognizerto make correspondence between the wafer numbers and plate number. Next,a polishing machine is used to rotate a plurality (4 in the illustratedexample) of plates having wafers bonded thereon together for theirpolishing. When the polishing is completed, a plate positioningmechanism 404 is used to detect the position of the marker M and tochange its rotary position relative to the reference position of themarker M in such a manner that the firstly bonded wafer comes at thefirst release position. After the position of the plate is modified sothat the firstly bonded wafer comes at a release mechanism 405, therelease mechanism 405 is operated to sequentially release the wafers intheir bonded order. And the released wafers are made associated with thenumber of the transport jig, the associated groove positions and thewafer numbers. Even in the releasing step, a bar code reader or imagereader 407 is used to read out the plate number and make correspondencebetween the plate number and wafer numbers. In this way, after the plateis positioned, wafers are sequentially released one after another in thebonded order, and then housed into the transport jig. Even at the timeof housing the wafers, the released wafers are sequentially housed oneafter another as associated with the number of the transport jig, groovepositions and wafer numbers.

In this way, the identification numbers of the wafers are correctlyheld.

Shown in FIG. 8 is an example of data showing relationships between thewafer numbers, plates and transport jigs. Under such a condition thatthe computer 41 for management of the lapping step made correspondencebetween the quality information and wafer numbers in this way, thecorrespondence information is transmitted to the computer 7.

In the cleaning step, the wafers are moved from the transport jig to acleaning jig and from the cleaning jig to the transport jig. FIG. 9shows a cleaning jig. In the case where a cleaning jig having a groovestructure similar to the transport jig is employed as shown in FIG. 9,if correspondence between the jig number and groove numbers are kept atthe time of moving the wafers from the transport jig to the cleaning jigand vice versa, the history of wafer movement can be managed.Accordingly, even in this step, the wafer identification number can bemaintained in the form of transport jig position.

Further, in the inspection step, transfer from one transport jig toanother transport jig is carried out as shown in FIG. 10. Even in thiscase, when management is carried out with the correspondence between thejig numbers and groove numbers kept, the wafer identification number canbe maintained. Reading of the jig number may be carried out by an imagereader. Further, a bar code may be used for indication of the jignumber.

When the each-wafer-basis quality information managed in this way arecollectively managed under control of the host computer through such acomputer network as shown in FIG. 1, the maintenance and effectivere-use of the information can be highly effectively realized.

Since the management is carried out not on each lot basis but on eachwafer basis, such a defect that is caused by a difference in processingcondition between the end and central parts of a jig e.g., in the heattreatment step can be easily found, whereby accurate correction can befacilitated and thus close management can be realized.

Although the present invention aims principally at the wafer qualitymanagement, the invention may be utilized even in physical distributionand cost control on each wafer basis.

Further, since history information is obtained at the end of each of thesteps and detection of a defect enables re-setting or re-adjustment ofconditions in the previous steps for its correction, modification of theconditions can be attained at an earlier stage and thus frequentoccurrence of defects can be prevented.

Furthermore, since the need for control based on each lot is eliminated,even when the next step corresponds to such a batch processing step as acleaning step or a chemical processing step, wafers can be transferredto the next step on each carrier basis, whereby a processing waste timecan be reduced and thus the invention can be effectively employed insmall number/multiple sorts of items production.

The present invention is not limited to such a specific embodiment forperforming management over all the steps as the foregoing embodiment,but management may be carried out only over part of the processingsteps.

INDUSTRIAL APPLICABILITY

As has been explained in the foregoing, in accordance with the presentinvention, the wafers cut out in the slicing step can be identified ineach of the steps up to the last-stage one on each wafer basis,operating conditions in each step can be accumulated in relation to eachwafer, wafer management can be realized in an accurate manner withoutdeteriorating the wafer quality.

We claim:
 1. An apparatus for manufacturing a plurality of semiconductorwafers, comprising:identification number applying means for setting anidentification number for each of the plurality of semiconductor wafers,said identification number corresponding to a location in a materialingot that a semiconductor wafer was cut from, and for storing theidentification numbers in a storage medium as identifier information;wafer information storing means for tracing as new identifierinformation a processing path indicative of how the wafer wastransferred and how the wafer was processed in each of manufacturingsteps on each wafer basis in association with the identifier informationin a previous step and for additionally storing the new identifierinformation as wafer information in the storage medium; and waferhistory management means for performing management over history of eachwafer from a lifting step for forming the material ingot throughoutentire wafer manufacturing steps on the basis of the stored waferinformation.
 2. An apparatus for manufacturing semiconductor wafers asset forth in claim 1, characterized in that the new identifierinformation is expressed in terms of wafer positional coordinates in ajig for accommodation of the wafer in each step.
 3. A method formanufacturing semiconductor wafers, comprising:a step of setting anidentification number for each of the semiconductor wafers, saididentification number corresponding to a location in a material ingotthat a semiconductor wafer was cut from, and of storing theidentification numbers in a storage medium as identifier information;and a wafer information additional storing step of tracing as newidentifier information a processing path indicative of how the wafer wastransferred and how the wafer was processed in each of manufacturingsteps on each wafer basis in association with the identifier informationin a previous step and of additionally storing the new identifierinformation as wafer information in the storage medium, characterized inthat management is carried out over history of each wafer from a liftingstep for forming the material ingot throughout entire wafermanufacturing steps on the basis of the stored wafer information.
 4. Amethod for manufacturing semiconductor wafers as set forth in claim 3,characterized in that the new identifier information is expressed interms of wafer positional coordinates in a jig for accommodation of thewafer in each step.